Mirage_Man
Flashlight Enthusiast
Anyone know the correct number for the 38mm Aleph window? I found a post that said it's a #31 but that seems a little big to me.
I use a metric size, 36mm x 3mm, in Buna-N. McMaster-Carr item # is 9262K295.
The Viton O-rings will be good for heat. One of the smaller ones is used in the AR-15 bolt to assist in extraction. This is subjected to noticable heat during long firing sequences. I would have no reservations about using that brand.
Boltgun
Use nitrile (buna-n) or viton. Either will work. The important thing is to get the proper interference fit. A minimum interference fit of .010 and a maximum fit of 0.28 is the range to work in. The Parker seal catalog is the standard reference on this.
The 70 durometer O-rings should work just fine. 90 durometer will work also, but will be harder to assemble.
Unless you have a special application, any source of O-rings should work. I buy from McMaster unless I need traceability. Then I go to a local seal specialist.
I used to run an elastomer testing lab. O-rings are easy once you learn how to design a proper seal glang.
underwatermike
Good job I read through the thread, it's more or less what I was going to say without mentioning any dimensions. The dimensions of the groove both radially and axially are critical if you wish to make an efficient seal. To get the correct size for an existing piece you can work back from the groove width and internal groove diameter. If you just want to stiffen a threaded part it's not near as critical. Not to mention backing rings .
Yes. And be aware neoprene O rings are different in that you can't use petroleum based lubricants with them. The rings can swell and make it difficult to unscrew the cap or head.
Use nitrile (buna-n) or viton. Either will work. The important thing is to get the proper interference fit. A minimum interference fit of .010 and a maximum fit of 0.28 is the range to work in. The Parker seal catalog is the standard reference on this.
The 70 durometer O-rings should work just fine. 90 durometer will work also, but will be harder to assemble.
Unless you have a special application, any source of O-rings should work. I buy from McMaster unless I need traceability. Then I go to a local seal specialist.
I used to run an elastomer testing lab. O-rings are easy once you learn how to design a proper seal glang.
underwatermike
That shows how long it's been since I've purchased a McG. I wasn't aware ...... McG's old lights like the PDs used the red silicone rings, but he has been using EPDM on the newer models for years.
The O-ring size is -210 (3/4" ID x 1" OD x 1/8" wide). The peg groove diameter is .800" & generally a 5% stretch is acceptable. These are stretched 6.6% so that might be one factor.... Also, your peg experiment has me curious. I have a bunch of buna-n rings I purchased for my McGs - I will put some outside to cook. My supposition is that those were either overstretched
Brand new in sealed package.or already dry rotted
I never wear work shoes on the bike. And the shifter pegs are contacted only when shifting, a small percentage of total time on a highway ride.or you had some nasties on your boots from the shop that killed them.
FWIW here's an unscientific test of Buna-N O-rings ...
I machined the Ti-6-4 shifter peg (below) for my H-D Road King. The Ti cylinder is grooved & Buna-N O-rings were installed as shown:
After less than 12 hours of outdoor exposure there was visible cracking on all O-rings. Then they started to break. Removed the remaining ones & installed silicone (red) O-rings. Can't detect any deterioration after 24 hours use & cost wasn't much more than Buna-N.